I had a patient come in today we treated her for peroneal tendonitis as her pain was on the outside of her foot at the base of the 5th metatarsal region.  But with the physical therapy her foot pain did not get better, it actually got worse.  

Sometimes if the tendon that inserts in the base of the 5th metatarsal or wraps around the cuboid bone can have another bone nearby.  This is called an accessory bone or ossicle.  Sometimes it can be near the bone and dislodged with a sprain of the foot.  

You can see the fracture of the bone here.  In order to make the diagnosis we need to have an MRI as my patient was not as clear as this.  Do you see the peroneal groove that is where the peroneus longus tendon runs.  
Here are some helpful websites to learn more about this condition:
To your health,
Dr. Donald Pelto